1. Field of the Invention
This invention relates to air handling equipment used to evacuate dust particles from cleanroom environment. More specifically, the invention relates to an air shower used to "rinse" or blow loose particles from a person entering the cleanroom environment.
2. Background of the Invention
Cleanrooms are manufacturing facilities which have reduced contamination, particularly from dust particles. Clean rooms have different degrees of cleanliness, ranging from Class 100 to Class 100,000, as measured by U.S. Federal Standard 209b. The establishment of higher cleanliness levels (lower class numbers) is accomplished by high efficiency air particulate (HEPA) filters.
Through a series of filtration and air flow control steps, dust particles are reduced from a typical ambient level of class one million (one million particles of one micron or larger per cubic foot) to levels which are from class one thousand (one thousand particles per cubic foot) and higher, down to class ten and lower. The cleanrooms from which this invention was developed are semiconductor fabrication facilities.
Apparatus of the general type with which this invention is concerned are used in conjunction with clean rooms such as semiconductor and pharmaceutical fabrication rooms, hospital operating rooms, and other rooms where it is important to provide an environment which is very low in particulates such as dirt, dust, skin cells and bacteria. In such rooms, workers often wear gloves and booties to prevent such particulates on their hands and feet from contaminating objects which the worker touches and to prevent such particulates from being shaken into the air from their hands and feet and randomly contaminating other objects in the room.
The semiconductor fabrication facility for which this invention was developed is a class one or zero cleanroom. The class one cleanroom atmosphere is maintained without the requirement that people in the cleanroom wear special breathing apparatus, although special clothing is required
In this type of cleanroom, a person entering the cleanroom would first pass a shoe-cleaning station and a sticky mat, and then enter a "bootie room." In that room, a person puts on shoe coverings ("booties") and a hair net. The person then passes through a first air shower and puts on the remaining cleanroom garments, including overalls, underhood, and gloves At that location, as well as in the bootie room and in other locations of the cleanroom facility, clean air is directed in a substantially vertical flow from the ceiling to , grates in the floor used for return air. The substantial portions of the cleanroom facility floor are grids which form the return air. By providing the vertical flow of air from the ceiling to the floor, dust particles which occur in the cleanroom facility are quickly drawn down through the return air. Other particle control techniques include a slight pressurization of the cleanroom facility in order that a door or other opening does not bring contaminated air into the cleanroom facility.
The air shower is used to remove loose particles from a person's skin and clothing prior to the person further entering the cleanroom facility. The air shower must perform two functions: first, the air shower must remove any loose particles from the user by blowing the particles from the user. Secondly, the air shower must evacuate or exhaust the particles which are generated by this process. For this reason, the air shower, while being turbulent, must also have a continuously directed air flow which is capable of exhausting particles removed by the turbulent action of the air shower. Air showers are used to remove particulates from gloved or ungloved hands, clad or unclad feet, hoods, jumpsuits, streetclothes, wipes and other objects by use of air streams. Ideally, air showers also prevent the removed particulates from re-entering the surrounding environment by trapping them (the particulates) in a filtration system.
Air showers generate different levels of comfort with different people, much as different individual dogs react differently to vacuum cleaners. In designing an air shower, we must be concerned with the maximum airflow tolerated by those who find the air shower least relaxing. Specifically, we desire that a maximum cleaning efficiency be achieved at a pleasant comfort level. We expect that a higher maximum airflow along a short length of corridor may be as pleasant as a lower maximum airflow along a longer length of corridor.
In the prior art, turbulent flow clean room systems were avoided in favor of clean room systems employing vertical laminar flow systems. Vertical laminar flow system clean room have planer inlet ports in the ceiling and outlet grates in the floor. Turbulent flow air showers, on the other hand, are very effective in removing loose particulates.
One type of air shower uses apertures which take the form of a pair of coplanar slots located in opposing walls, and extend vertically from a point approximately 0.5 meters high to a point approximately 1.5 meters high. To correctly utilize this type of air shower, a worker opens the entrance door, enters the shower room, positions himself or herself between the slots, raises his or her arms and turns in a complete circle. The blower forces a stream of generally laminar medium velocity air through each slot, into the shower room and against the person to dislodge particles from the person's body. Some of the particulates are immediately entrained in the return flow of air and drawn through the floor and the filter, and other of the dislodged particulates float into the air within the shower room, are contained by the walls and ceiling of the shower room and most are eventually entrained in the return flow of air and filtered. Some of these other particulates may escape from the shower room when the worker exits. An air curtain is provided to block the dislodged particulates so that the dislodged particulates do not enter the surrounding environment. Consequently, such a device is usually installed outside of a clean room. The air curtains occur as a natural effect of the air flow patterns which occur in various portions of the clean room, and usually are not specially installed.
Another similar type of air shower uses a group of nozzles located on the ceiling and walls of the associated shower room instead of the vertical slots to direct streams of air against a user.
The process of utilizing the air showers of the types described above, from the time the user opens the entrance door to the time the worker exits the shower room, usually requires 30 seconds or more and is inconvenient.
It is a general aim of the invention to provide a cleaning apparatus of the foregoing type which removes the particulates quickly with minimal inconvenience to the user. At the same time it is desired to prepare the user for entrance into the clean room by putting the user in a proper state of mind.